When using a light source to illuminate transparencies which are to be printed, it is often desirable to change the balance of the primary color components of the light from the source to achieve a desired color balance in the final print. When additive printing processes are employed, the primary colors utilized are red, blue and green. It is known to utilize three light sources, one for each primary color, to independently attenuate the light from these sources and then combine the component beams to form a beam of color compensated white light. It is also known to derive the color compensated white light from a single light source by splitting off individual primary color component beams one after the other proceeding along the optical path of the light, and individually attenuating each component beam.
The known lamphouses are characterized by various disadvantages relating to the efficiency of the utilization of the light from the source, the equality of the three component beams, and other factors.